This invention relates generally to dental instruments and, more particularly, to an instrument for carrying and dispensing dental amalgam for use in connection with depositing the amalgam in tooth cavities.
Amalgam carriers and dispensers have in the past taken many different forms. For example, various dental amalgam carriers and dispensers are illustrated in the following U.S. patents: U.S. Pat. Nos. 1,797,866; U.S. Pat. No. 2,503,156; U.S. Pat. No. 2,679,102; U.S. Pat. No. 3,221,409; U.S. Pat. No. 3,091,860 and U.S. Pat. No. 3,537,617.
Generally, conventional amalgam carriers and dispensers include apparatus wherein a plunger, formed of a metallic material such as stainless steel, is slideably located within the internal bore of a sleeve. The plunger is normally located so that its forward end surface is recessed within the bore so as to define a cavity or space within the sleeve into which the amalgam is condensed or packed. The dentist then locates the instrument such that the amalgam filled sleeve is within the tooth cavity to be treated, the latter having been previously prepared such as by drilling, whereupon appropriate levers are actuated to cause the plunger to move axially within the sleeve bore so that the terminal end region of the plunger extends beyond the open end of the sleeve bore thereby expelling or dispensing the amalgam into the tooth cavity.
Such conventional amalgam carriers and dispensers, however, are not entirely satisfactory. More particular, conventional amalgams, which usually comprise alloys of mercury with one or more of tin, cadmium, silver, and/or copper in cut or spherical particle design are extremely hard materials. Further, in recent years, amalgams have been formulated in a manner such that their hardness has been increased to an even greater extent. Such modern amalgams comprise copper phase, dispersed phase, ternary, spherical and spherical blend alloys in combination with mercury. Due to the hardness of conventional and modern day amalgams, it has been found that the surfaces of the components of conventional amalgam carriers which come into contact with such amalgams become severely abraded during use and consequently tend to wear at a fast rate.
More particularly, as noted above, the amalgam is condensed or packed into the sleeve recess or cavity prior to its being dispensed whereupon the plunger is moved forwardly to introduce amalgam into the tooth cavity. However, a small amount of the amalgam tends to remain within the sleeve in the clearance space between the plunger and sleeve which abrades the surface of the plunger and sleeve, causing undersirable striations to be formed in these surfaces during use. With continued usage of the instrument, these surfaces are further abraded and the clearance space between the plunger and bore surface unavoidably increases to a point where the instrument becomes unusable. For example, as the clearance between the plunger and internal bore surface increases, the possibility of the plunger binding within the sleeve increases, and, further, when the plunger is actuated to expel the amalgam, increasing amounts of the latter tend to remain within the sleeve in the continuously enlarging clearance space between the plunger and sleeve. For these reasons, conventional amalgam carriers and dispensers must be periodically replaced at relatively short intervals.
Attempts have been made to overcome the problems discussed above. For example, in U.S. Pat. No. 2,903,794, an amalgam carrier is illustrated comprising a plunger disposed within a sleeve, the plunger comprising an outer portion and an inner portion formed of a flexible material, such as Teflon. However, these attempts have not alleviated the problem. Such instruments are also not acceptable since their tactile feel is quite different from that to which dentists are normally accustomed. Further, attempts have been made to overcome the problem by reducing the clearance between the plunger and sleeve. It has been found that these attempts, rather than alleviating the problem, have aggravated the same by increasing the abrasion.